Holt told supporters in an email Tuesday he wanted to pursue other projects, which he didn't spell out, and that there wasn't a "hidden motive" for his decision to leave at the end of his term, the Hill reported.

"As friends who have worked with me know, I have never thought that the primary purpose of my work was re-election and I have never intended to make service in the House my entire career," Holt said. "For a variety of reasons, personal and professional, all of them positive and optimistic, the end of this year seems to me to be the right time to step aside and ask the voters to select the next representative."

Last year, he was unsuccessful in an attempt to win the U.S. Senate seat left vacant by the death of Frank Lautenberg.

President Obama weighed in on Holt's performance in the House, saying he "combined a relentless focus on building a brighter future with an unwavering commitment to improving the everyday lives of the New Jerseyans he represents, especially the veterans he works tirelessly to support."

"Just the second research physicist elected to Congress, no one has worked harder to keep America on the cutting edge of innovation than Rush," Obama said. "Time and time again, he has led efforts to fund science education and basic research. His legacy will live on in our labs, our universities, and our classrooms, where countless math and science teachers have been able to afford college thanks in part to the TEACH grants he helped create."

Holt -- a former physics and public policy professor who once was a contestant on the answer-and-question game show "Jeopardy!" --was first elected to represent New Jersey's Democrat-leaning 12th Congressional District in 1998. His academic background inspired the bumper sticker "My congressman IS a rocket scientist."

He consistently sought money for scientific research and improved science education, securing $22 billion for research in the stimulus bill, the New York Times reported. He also sought grant funding for students studying to teach math, science or foreign languages, the New York Times reported.

In an interview with the Times, Holt, 65, called Congress "the greatest instrument for justice and human welfare in the world," even with its foibles.

"The stories trying to puzzle out why someone would do something else are based on this rather narrow way of thinking that the only purpose for a member of Congress is to be re-elected," Holt said. "I've never viewed it that way, and I think everybody who's worked with me knows that I think there are a lot of things that I can and should be doing."

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